Ayoub BENSAKHRIA · @ayoubbensakhria. Toxicologist. analyticaltoxicology. com. Joined September Metal and metalloid biotransformations in South African acid mine drainage systems” .. la présence de composés très toxiques comme le plomb, l’arsenic ou le. d’effets toxiques précoces et tardifs pour des molécules En effet, les poissons étant capables de biotransformation, ils peuvent donc.
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Skip to main content. Log In Sign Up. Biotransformation of the Streptomyces scabies phytotoxin thaxtomin A by the fungus Aspergillus niger. George Lazarovits Larry A. Unraveling the microbiome of corn View project Molecular and cytological characterization of biocontrol metabolites produced by plant growth promoting rhizobacteria View project All content following this page was uploaded by George Lazarovits on 16 July King, and Larry A.
Of several hundred microorganisms randomly selected from the environment, only a fungal isolate identified as Aspergillus niger van Tiegham var. The rate and extent of transformation of thaxtomin A was tested under a variety of conditions, including dif- ferent growth media, biomass concentrations, incubation periods, and shaker speeds.
Under optimum conditions the fungus converted thaxtomin A into two major and five minor metabolites. The two major metabolites and three of the five minor metabolites were fully characterized by a combination of mass spectral and nuclear magnetic resonance techniques.
When assayed on aseptically produced mini-tubers, the major metabolites proved to be much less phytotoxic than thaxtomin A. Aspergillus niger van Tiegham var.
Scab lesions fection by the soil bacterium Streptomyces scabies, is con- may be superficial, erumpent, or pitted and thereby cause di- sidered a disease of major economic importance in many rect losses to growers by reducing tuber marketability. In- Methods of containment biotranformation generally inadequate or incon- fection occurs mainly through the lenticels of immature tu- sistent McKenna et al.
The present study was initi- ated to explore control technologies based on the involvement of phytotoxins as essential factors in the dis- Received 14 August Revision received 20 November A number of studies Press Web site at http: The best example of this approach for L. When the gene Fig. This eliminated symptoms and hence crop damage Zhang et al. The phytotoxins associated with common scab of potato disease consist of biotransforation containing dioxo- piperazines, and thaxtomin A Fig.
Synthetic studies related to the structural determinations confirmed that the presence of a C-4 nitro and a C phenyl moiety are requi- sites for phytotoxicity in these compounds King et al. Controls received absolute ethanol only.
Five- bioactivity King et al. In initial endeavours to ascer- millilitre volumes of the nutrient media were pipetted into tain if biological detoxification of thaxtomin A was possible, sterile mL Erlenmeyer flasks for testing thaxtomin A various bacteria of unknown classification were screened for transformations.
Samples were taken at various biotransforamtion effect. In these preliminary studies performed using mini- from 1 to 14 days after inoculation. For assessment of fungal acteristic yellow colour of thaxtomin A in the medium or by growth, triplicate 5-mL samples were filtered through a thin-layer chromatography TLC studies of medium ex- preweighed Whatman No.
The tent in their activity. We also tested a large number of fungal pH of the filtrates was measured using a pH meter.
Toxic biotransformations – definition of toxic biotransformations by The Free Dictionary
The me- isolates toxiwues from rotting wood. These fungi were con- dia were then extracted with equivalent volumes of ethyl ac- sidered most likely to have lignin-degrading abilities and the etate. In some experiments, Nishino and Spain In this toxiquse we describe the pu- the replications of each treatment were bulked before analy- rification, characterization, and relative bioactivity of metab- sis and in others they were analyzed individually.
Generally, olites resulting from the biotransformation of thaxtomin A after 1 week of incubation on a shaker, the thaxtomin A con- by a fungus isolated from the bark of a decomposing decidu- centration was either much reduced or it was not detectable ees tree likely beech. The fungal isolate was identified by on silica gel TLC analysis of the ethyl acetate extracts.
In contrast, thaxtomin A Tiegham var.
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This method does not completely dis- time. Fractionation of the transformed thaxtomin A extracts tinguish A. The band extracts were further separated on Transformation tests and metabolite isolation silica gel TLC plates to yield various amounts of seven new A single-spore isolate of the fungus and subcultures were metabolites.
Both methods utilized retained the 4-nitroindole moiety. Table 1 summarizes chro- ously King and Lawrence ; Goyer et al.
The ef- matographic and molecular weight data for the metabolites. This provided a concentration of for 7 and 10 days, respectively. The transformation of 0. Summary of molecular weight MW and chromatographic data for thaxtomin A transformation products M-1 to M HPLC, high-performance liquid chromatography. Mycelial dry weight, media pH, and relative percentage of conversion products of thaxtomin A over 4 days incubation of Aspergillus niger in one-quarter strength potato dextrose broth containing 0.
Mean of three replications of two separate experiments. The experiment was carried out four times with similar trends in the results. Values in parentheses are the standard error. Similarly, extracts from full- and half-strength 1. This may also have contributed to PDB under both shaking and still conditions also contained the low levels of fungal growth in this biotransformatino and to perhaps compounds that migrated with thaxtomin A and metabolites.
Inoculum levels also influ- 7. The relative proportions of these metabolites biotransfor,ation not enced the rate of thaxtomin A transformation.
With the low- change significantly after 4 days of incubation Table 2. Only in a few instances did lation.
By day 3, however, such cultures had significant the fungus completely eliminate thaxtomin A from the cul- amounts of M When higher spore levels were used ture filtrate. Occasionally, however, even some of the higher dos- al. When applied at concentrations as amount of thaxtomin A present at day 3.
The maximum Metabolite identification fungal dry weight of 18—21 mg was obtained by day 3 in In characterization of the thaxtomin A transformation both the presence and absence of thaxtomin A Table 2. The products, mass spectral data for the major metabolite M-5 dry weights of the ethyl acetate extracts from such cultures indicated it to be a probable dehydration or cyclodehydration ranged from about 4 to 14 mg by day 5. The pH of the me- analog of thaxtomin A see Table 1. Numbers refer to carbons correlated to the hydrogen at the position listed in the first column.
Structural formula of metabolite M Structural formulas of metabolites M-2 and M Mass spectral data for the only other metabolite of significant yield, i. In the process of repurifying the M-3 sample after 1H to the eventual dehydration products M-3 and M The ex- NMR studies, it was discovered that some conversion to the ceptional loss of bioactivity observed for M-5 is assumed a M-2 Fig.
A subsequent compar- reflection of its substantially revamped structure in compari- ative 1H NMR analysis Table 4 of M-2 indicated it to be a son with thaxtomin A and is a prime example biofransformation the poten- C conformer Fig.
Of the biotrxnsformation remaining me- tial for biocontrol stratagems based on phytotoxin tabolites, only two, i. A comparison of their respective 1H Acknowledgements NMR spectra Table 5 demonstrated essential differences only in the C substituents, i. Quantitative relationships among thaxtomin A production, potato scab severity, and fatty acid composition goxiques Streptomyces.
Plant pathogenicity biotraansformation the genus Streptomyces. More gene manipulations in A quan- Novel in vivo use of polyvalent Streptomyces phage to disinfest titative method for determining soil populations of Streptomyces Streptomyces scabies-infected seed potatoes.
Biodegradation and transfor- Goyer, C. Pathogenicity of mation of nitroaromatic compounds. In Manual of environmen- Streptomyces scabies mutants altered in thaxtomin A produc- tal microbiology. American Society for tion. The txtAB genes of the plant pathogen Streptomyces destruxins: Patent Office 30 pages. Detoxification of fusaric acid by a fusaric acid-resistant Streptomyces scabies.
Magnaporthe bies isolates from scab infected potato tubers. Potato grisea genes for pathogenicity and virulence identified through Assoc. The gene for albicidin detoxifica- of phytotoxins associated with Streptomyces scabies, the causal tion from Pantoea dispersa encodes an esterase and attenuates organism of potato common scab.
Engineered detoxification glucosylation of thaxtomin A, a partial detoxification. Remember me on this computer. botransformation
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